Cyclotron



Feb. 1, 1955 T. M. DICKINSON CYCLOTRON 2 Sheets-Sheet 1 Filed May 31,1951 IIIII Inventor- Theodore M. Dickinson,

His Attorneg.

T. M. DICKINSON 2,701,304

Feb. 1, 1955 CYCLOTRON Filed May 51, 1951 2 Sheets-Sheet 2 Fig.5.

J6 W 45187 5/ 45 40' 52 l I I J5"- F F Fig.5.

pM/QW H is Attorney.

United States Patent CYCLOTRON Theodore M. Dickinson, Schenectady, N.Y., assignor to General Electric Company, a corporation of New YorkApplication May 31, 1951, Serial No. 229,077

Claims. (Cl. 25027) This invention relates generally to cyclotronapparatus for accelerating charged particles in spiral paths, andparticularly to means for energizing such apparatus.

In cyclotron apparatus, ions are accelerated to high energy levels inspiral paths by the combined action of a cyclically reversible electricfield and a unidirectional magnetic field. One of the most familiarforms of this apparatus comprises a pair of opposed hollow, D-shapedelectrodes, called dees, enclosed by an evacuable tank and energized bya suitable source of oscillatory power. Ions formed in the central spacebetween the dee electrodes are accelerated intermittently by thereversible electric field appearing between the dee electrodes, whilethey are simultaneously constrained to outwardly spiraling paths by theunidirectional magnetic field which is oriented to be essentially normalto the plane of extension of the dee electrodes.

One of the primary problems encountered in the construction of cyclotronapparatus has been that of obtaining suitable means for energizing thedee electrodes. In order to secure the required high voltage andfrequency stability, the dee electrodes are usually supported at theends of transmission lines, whereby the lines with the dee electrodesconnected thereto serve as a high Q tank circuit for an electrondischarge tube oscillator. While this expedient has provided adequatehigh voltage and frequency stability, the coupling of the oscillator tothe transmission lines has caused considerable difliculty, since thetransmission lines have a tendency to oscillate in such a mode that noelectric field appears between the dee electrodes. Therefore, it is aprincipal object of the present invention to provide improved means forenergizing the dee electrodes in cyclotron apparatus.

According to one aspect of the invention, more fully described anddelineated hereinafter, there is provided cyclotron apparatus having apair of dee electrodes connected to a parallel wire transmission line.The dee electrodes are energized by an electron discharge tubeoscillator which is inductively coupled to the transmission line in suchmanner as to assure the production of the desired electric field betweenthe dee electrodes.

The aspects of my invention which I desire to protect herein are pointedout with particularity in the appended claims. The invention itself,together with further objects and advantages thereof, may best beunderstood by reference to the following description, taken inconnection with the accompanying drawings, in which Fig. 1 is aschematic, partially broken away, perspective view of cyclotronapparatus suitably embodying the invention; Fig. 2 is a fragmentarysectional view taken along line 22 of Fig. 1; Fig. 3 is a circuitdiagram illustrating preferred connections for the energization of theapparatus of Fig. 1; and Figs. 4, 5 are diagrammatic representationsuseful in explaining the invention. To facilitate the description of theinvention, like numerals will be employed to identify similar elementsin the various figures of the drawings.

Referring now to Figs. 1 and 2, there is shown cyclotron apparatus whichcomprises opposed, hollow, dee electrodes 1 and 2, suitably supported atthe ends of hollow transmission lines 3 and 4, within an evacuable,hollow tank 5. Portion 6 of tank 5 and portions 7, 8 of transmissionlines 3, 4, respectively, are reduced in the height dimension in orderto facilitate the insertion of this section of the apparatus between thepole pieces of an electromagnet, not shown, whereby a magnetic fieldhaving a direction as indicated by the arrow H, essen- 2,701,304Patented Feb. 1, 1955 "ice tially normal to the plane of extension ofdee electrodes 1 and 2, may be provided. According to well knownprinciples of cyclotron operation, if the dee electrodes are energizedsuch that a cyclically reversible electric field appears therebetweenand if ions are generated in the central space within the deeelectrodes, the ions will be repetitively accelerated in outwardlyspiraling paths as they traverse the space between dee electrodes 1 and2. In such fashion, ions may be accelerated to high energy levels andutilized for various purposes well known to those skilled in the art. Amore detailed description of the principle of operation of cyclotronapparatus may be found in U. S. Patent 1,948,384-E. 0. Lawrence, datedFebruary 20, 1934, or in the monograph entitled The Cyclotron by W. B.Mann, published by Methuen & Company, Ltd., London, England.

In order to energize dee electrodes 1 and 2 according to the inventionto produce the desired cyclically reversible electric fieldtherebetween, an electron discharge tube oscillator is coupled totransmission lines 3 and 4 by means of an anode loop 9 and a cathodefeedback loop 10. Anode loop 9 is adjustably supported betweentransmission lines 3 and 4 by means of conductive rods 11 and 12, whichare slidably inserted through hermetic sealing insulators 13 and 14. Atthe upper ends of rods 11 and 12 respectively are attached clamp members15 and 16, which serve as electrical connections for the anodes 19 and20 of electron discharge devices 17 and 18 respectively. For a purposethat will be more fully described hereinafter, a center tap is providedfor anode loop 9 by means of right-angle conductive rod 21, which isintroduced to tank 5 in slidable hermetic relationship by means of aninsulator 22. Cathode loop 10 is supported in a manner similar to anodeloop 9 by means of conductive rods 23, 24 and insulators 25, 26. Afiixedto the upper ends of conductive rods 23, 24 respectively are rods 27 and28, the former of which is connected through a flexible lead 29 to oneside of the filament of discharge tube 17 and the latter of which isconnected through a flexible lead 30 to one side of the filament ofdischarge tube 18. In order to decrease the likelihood of undesiredoscillations during operation of the apparatus, an electrostatic shield31 is provided as shown; and the discharge tube oscillator is surroundedby a shield 32 to prevent the generated oscillations from radiating anddisturbing nearby equipment.

A better understanding of the electrical interconnections of theelectronic oscillator of the invention may be had by reference to thecircuit diagram of Fig. 3. As has been mentioned heretofore, anode loop9 is connected at one end to the plate electrode 19 of discharge tube 17and at the other end to the plate electrode 20 of discharge tube 18;while cathode loop 10 is connected at one end to one side of thefilament 35 of discharge tube 17 and at the other end to one side of thefilament 36 of discharge tube 18. Anode loop 9 and cathode loop 10 arerespectively shunted by variable tuning capacitors 37 and 38; and thepositive terminal of the B voltage supply, which is connected to groundas indicated conventionally at 39, is introduced into the oscillatorcircuit at the approximate mid-point 40 of anode loop 9 through anisolating high frequency choke 41a. Alternating heating current issupplied to filaments 35 and 36 from a source of alternating current 41connected to the primary winding 42 of a filament transformer 43.Current induced in secondary winding 44 of filament transformer 43 isdirected to filaments 35 and 36 through a network including highfrequency choke coils 45, 46, 47, 48, and bypass capacitors 49, 50, 51,52. The center tap 53 of secondary winding 44 is connected through ahigh frequency choke 54 to the minus terminal of the B voltage supplyand also through a parallel network, including a crate to generatesustained oscillations within the tank circuit formed by transmissionlines 3, 4, and dee electrodes 1, 2. Tuning bar 61, which may beelectrically connected through sliding contacts, not shown, totransmission lines 3 and 4 and the inside conducting surface of tank 5as represented schematically in Fig. 1, may be adjusted through anoperating rod 62 such that a desired condition of resonance obtains atthe operating frequency of the cyclotron apparatus, whereby transmissionlines 3 and 4 may be considered as a shielded parallel wire transmissionline having effectively a foreshortened quarter wavelength. Tuningcapacitors 37 and 38 may be employed to adjust the relative phases ofvoltages induced in anode loop 9 and cathode loop 10. By varying theheight of anode loop 9 in conjunction with the adjustment of tuningcapacitor 37, the anode loop may be tuned for an impedance match to theload impedance reflected thereinto; and by varying the height of cathodeloop 10 in conjunction with the adjustment of tuning capacitor 38, thecathode loop may be tuned for the proper amplitude of feedback voltageto sustain tank circuit oscillation.

It will be realized from the foregoing that, in order to obtain thedesired cyclically reversible electric field between dee electrodes 1and 2, oscillations must occur whereby transmission lines 3 and 4oscillate in the opposite phase, i. e., electron discharge devices 17and 18 must operate in push-pull to produce coincident, relativelyopposite polarities of transmission lines 3 and 4. The diagrammaticillustrations of Figs. 4 and 5 show that, with the arrangement of anodeloop 9 and cathode loop 10 relative to transmission lines 3 and 4according to the invention as hereinbefore described, oscillations canoccur only in the desired mode with transmission lines 3 and 4 havingopposite phases. If, for example, transmission lines 3 and 4 tend tooscillate in phase, the currents in both transmission lines travel inthe same direction as is indicated in Fig. 4. In this instance, themagnetic field lines encircle both transmission lines 3 and 4 somewhatas represented by the lines labeled H in Fig. 4, whereby there is nochanging magnetic field linking anode loop 9 or cathode loop 10 (notshown), and power can neither be transferred to transmission lines 3, 4from anode loop 9 nor can power be removed for grid-cathode excitationby cathode loop 10. Consequently, when transmission lines 3 and 4 tendto oscillate in phase, oscillations cannot persist. However, whentransmission lines 3 and 4 oscillate in the out-of-phase mode, themagnetic field lines will appear somewhat as represented by the lineslabeled H in Fig. 5. In this situation, the magnetic field encirclingtransmission line 3 has a clockwise direction, while that encirclingtransmission line 4 has a counterclockwise direction, whereby the twofields are additive in between the lines. Therefore, the magnetic fieldlines link both anode loop 9 and cathode loop 10, and oscillations willbe built up as desired. Moreover, by placing both loops 9 and 10 inessentially the same plane as shown in Fig. 1, tendency for oscillationto occur by virtue of magnetic coupling between them is eliminated, andoscillation can only occur by virtue of coupling through the resonantline and dee system.

It will be understood by those skilled in the art that the invention maybe modified substantially without departing from the spirit of theinvention. For example, instead of maintaining grids 58 and 59 at a highfrequency ground potential, filaments 35 and 36 may be maintained atsubstantially high frequency ground potential. With such a circuitmodification, a grid feedback loop would be substituted for the cathodefeedback loop of the circuit of Fig. 3 and the orientation would be suchthat open ends of the anode and grid loops are adjacent each other.However, the grounded grid circuit of Fig. 3 is preferred becausedifficult neutralization of undesired oscillations is necessary in thegrounded cathode circuit. As another exemplary modification, ahermetically sealed partition may be utilized within tank 5 to seal offthe dee electrodes from the remainder of tank interior in order toreduce the volume requiring evacuation.

What I claim as new and desire to secure by Letters Patent in the UnitedStates is:

1. Cyclotron apparatus comprising a pair of dee electrodes between whicha cyclically reversible electric field may be developed for acceleratingcharged particles in spiral paths, means for energizing the deeelectrodes comprising a parallel wire transmission line connected tosaid dee electrodes, and an electron discharge tube oscillatorinductively coupled to said parallel wire transmission line, saidtransmission line with said dee electrodes connected thereto being aforeshortened quarter wavelength at the operating frequency of saidoscillator, said inductive coupling of said oscillator including ananode loop and a feedback loop both extending in planes essentiallyparallel to the plane of extension of said transmission line andpositioned intermediate said parallel wire transmission lines.

2. Cyclotron apparatus comprising a pair of dee electrodes between whicha cyclically reversible electric field may be developed for acceleratingcharged particles in spiral paths, means for energizing the deeelectrodes comprising a shielded parallel wire transmission lineconnected to said dee electrodes, and an electron discharge tubeoscillator inductively coupled to said parallel wire transmission line,said transmission line with said dee electrodes connected thereto beinga foreshortened quarter wavelength at the operating frequency of saidoscillator, said inductive coupling of said oscillator including ananode loop and a feedback loop both extending in planes essentiallyparallel to the plane of extension of said transmission line andpositioned intermediate said parallel wire transmission lines.

3. Apparatus as in claim 1 in which said feedback loop comprises acathode loop, said anode and cathode loops being positioned with theopen end of one of the loops adjacent the closed end of the other of theloops.

4. Cyclotron apparatus for accelerating charged particles comprising apair of dee electrodes, an electron discharge tube oscillator forenergizing said dee electrodes, a pair of hollow conductors each ofwhich is connected at one end to one of said pair of dee electrodes,said conductors and said dee electrodes being enclosed by an evacuabletank of conductive material, said pair of conductors with said deeelectrodes connected thereto being a foreshortened quarter wave-lengthat the operating frequency of said oscillator and means hermeticallyintroduced into said tank for coupling said oscillator to said hollowconductors including an anode loop and a feedback loop both extending inplanes essentially parallel to a plane including the longitudinal axesof said conductors and positioned intermediate said pair of hollowconductors.

5. Cyclotron apparatus for accelerating charged particles comprising apair of dee electrodes, a push-pull electron discharge tube oscillatorfor energizing said dee electrodes, a pair of hollow conductors each ofwhich is connected at one end to one of said pair of dee electrodes,said conductors and said dee electrodes being enclosed by an evacuabletank of conductive material, means coupled to said conductors for tuningsaid conductors and said dee electrodes to a foreshortened quarterwave-length at the operating frequency of said oscillator and means forcoupling said oscillator to said conductors including an anode loop anda feedback loop both extending in planes essentially parallel to a planeincluding the longitudinal axes of said conductors and positionedintermediate said pair of hollow conductors.

References Cited in the file of this patent UNITED STATES PATENTS

